Lipoprotein lipase (LPL), hepatic lipase (HL) and endothelial lipase (EL) have long been appreciated as important biochemical players in triglyceride (TG) and cholesterol metabolism. More recently, these lipases emerged as some ofthe strongest genetic determinants of plasma TG and HDL cholesterol levels in the general population. Dysregulation of LPL results in pathological changes associated with the Metabolic Syndrome, including dyslipidemia, insulin resistance, cardiomyopathy and beta-cell dysfunction. Although much ofthe physiological regulation of LPL activity occurs at the post-translational level, the underlying molecular mechanisms have been poorly understood. In the current PPG cycle we identified a novel factor, Lipase Maturation Factor 1 (Lmf1), which facilitates the folding, assembly and secretion of lipases. While Lmf1 is clearly required for lipase expression, the metabolic consequences of combined lipase deficiency in the adult organism, and the molecular function of Lmf1 remain unexplored. Three aims will be pursued to address these issues. In Aim 1, we will generate and characterize conditional and tissue-specific knock-out mouse models to investigate the role of Lmf1 in systemic and adipose metabolism. To extend these studies to humans in Aim 2, we will identify variants associated with fasting or postprandial plasma TG levels by resequencing LMFI in various populations. Furthermore, naturally occurring variants affecting Lmf1 expression in inbred mouse strains will be exploited to address the role of this protein in lipid metabolism and related traits. In Aim 3, we will investigate the molecular aspects of Lmf1 function by identifying the proteome of Lmf1-interacting factors using genetic and biochemical approaches.